1. Field of the Invention
This invention relates to the repair of superalloy components and in particular, to superalloy components used in gas turbines, and most particularly, to low melting point braze alloys for repair of such superalloy components.
2. Background and Related Art
Superalloys are typically understood to be high-temperature materials which display excellent resistance to mechanical and chemical degradation of properties even as temperatures approach the melting points of the materials. Ni superalloys are based upon nickel (Ni) and typically contain significant amounts of numerous other elements such as chromium (Cr), aluminum (Al), titanium (Ti), tungsten (W), cobalt (Co), tantalum (Ta), carbon (C), among others. The high-temperature performance of superalloys found early application in aircraft turbine engines. Since a higher operating temperature typically leads to increased fuel efficiency and lower carbon emissions, this caused superalloys to find increasing uses in ground-based turbine systems as well. For example, see The Superalloys, by Roger C. Reed, (Cambridge University Press, 2006, particularly Chapter 1). The entire content of this reference is incorporated herein by reference for all purposes.
Thus, as superalloys are used in greater numbers of airborne and ground-based turbine systems, and operated at higher temperatures, increasing numbers of blades, vanes and other components are subject to cracking and other forms of material degradation requiring repair. It is important that the repair of such turbine components be effectively carried out to result in repaired components having properties as close as possible to those of the original components.
Brazing is one important technique for repairing cracks in superalloy components that basically involves the use of a filler material introduced into the crack to be repaired, subsequently heated so as to form a bond or to repair the crack. While many brazing filler materials have been investigated, a need exists in the art for improved brazing filler materials producing better structural properties in the repaired component, reduces or avoids the formation of deleterious phases in the repaired component, is sufficiently robust for the repaired component to survive subsequent processing without serious degradation of properties, the brazing alloy melts at temperatures below the solidus of the base metal, among other characteristics required of, or desirable in, a brazing alloy and the repaired superalloy components.